netdev - Re: [PATCH v2 net] mlx4_core: restore optimal ICM memory allocation

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Message-Id: <20180603.110220.498973436322342400.davem@davemloft.net>
Date:   Sun, 03 Jun 2018 11:02:20 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        jsperbeck@...gle.com, tarick@...gle.com, qing.huang@...cle.com,
        danielj@...lanox.com, yanjun.zhu@...cle.com
Subject: Re: [PATCH v2 net] mlx4_core: restore optimal ICM memory allocation

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu, 31 May 2018 05:52:24 -0700

> Commit 1383cb8103bb ("mlx4_core: allocate ICM memory in page size chunks")
> brought two regressions caught in our regression suite.
> 
> The big one is an additional cost of 256 bytes of overhead per 4096 bytes,
> or 6.25 % which is unacceptable since ICM can be pretty large.
> 
> This comes from having to allocate one struct mlx4_icm_chunk (256 bytes)
> per MLX4_TABLE_CHUNK, which the buggy commit shrank to 4KB
> (instead of prior 256KB)
> 
> Note that mlx4_alloc_icm() is already able to try high order allocations
> and fallback to low-order allocations under high memory pressure.
> 
> Most of these allocations happen right after boot time, when we get
> plenty of non fragmented memory, there is really no point being so
> pessimistic and break huge pages into order-0 ones just for fun.
> 
> We only have to tweak gfp_mask a bit, to help falling back faster,
> without risking OOM killings.
> 
> Second regression is an KASAN fault, that will need further investigations.
> 
> Fixes: 1383cb8103bb ("mlx4_core: allocate ICM memory in page size chunks")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Tariq Toukan <tariqt@...lanox.com>

Applied, thanks Eric.